Traditionally, semiconductor materials, such as silicon, have been used to implement memory circuits. Typically, the semiconductor materials are used in combination with dielectric and conductive materials to fashion transistors, capacitors, resistors, inductors and other basic circuit elements, which are arranged in various combinations to form memory cells and other components of memory devices.
Other types of materials are currently being investigated to replace semiconductor materials in memory devices and other electronics applications, due to the ongoing desire to produce electronic devices with greater information storage density, lower cost, higher speed, and/or other desirable characteristics. Such new materials may include organic molecular materials that can store information by taking on various oxidation states in response to applied signals. Such materials offer potentially higher component density, response speeds, and/or energy efficiency in memory applications.
A variety of approaches have been proposed for such molecular memory devices. For example, ZettaRAM™ is an emerging technology which may replace conventional dynamic random-access memory (DRAM) in computer and/or other memory systems. In ZettaRAM™, the conventional capacitor in a DRAM cell may be replaced with “charge-storage” molecules to form a molecular capacitor. The amount of charge stored in the molecular capacitor is independent of write voltage. In other words, there is a predetermined threshold voltage above which the device stores a fixed amount of charge, and below which the device discharges the fixed amount of charge. A logical “1” may be written by charging the molecules at a voltage above the threshold voltage, also called programming. A logical “0” may be written by discharging the molecules at a voltage below the threshold voltage, also called erasing. Further description of molecular memory devices can be found in U.S. Pat. No. 6,212,093 to Lindsey, U.S. Pat. No. 6,272,038 to Clausen et al., and U.S. Patent Application Publication No. 2004/0120180 to Rotenberg et al.
Recently, numerous studies have been performed on energy management in memory systems. Low-power memory systems may be desirable for a wide range of computers and other electronics, such as cell phones, personal digital assistants (PDAs), portable consumer electronics, laptops, and/or other battery-constrained electronic devices. For example, energy management schemes have been proposed based on switching between different device operating modes, such as active, standby, nap, and power-down. Additional description of such energy management schemes can be found in “Scheduler-based DRAM Energy Management” by V. Delaluz, A. Sivasubramaniam, M. Kandemir, N. Vijaykrishnan, and M. J. Irwin, Design Automation Conference, June 2002, and in “Memory Controller Policies for DRAM Power Management” by X. Fan, C. S. Ellis, and A. R. Lebeck, Int'l Symposium on Low Power Electronics and Design, August 2001.
Also, techniques have been proposed to reduce row-buffer conflicts and increase row buffer hit rates, such as those described in “A Permutation-based Page Interleaving Scheme to Reduce Row-buffer Conflicts and Exploit Data Locality” by Z. Zhang, Z. Zhu, and X. Zhang, 33rd Int'l Symposium on Microarchitecture, December 2000, pp. 32–41. This in turn may result in fewer bitline state transitions, because data may remain in the row buffer for a longer period of time. As recognized in “Trends in Low-Power RAM Circuit Technologies” by K. Itoh, K. Sasaki, and Y. Nakagome, Proc. of the IEEE, 83(4), April 1995, pp. 524–543, bitline energy consumption may be a major component of total memory system energy consumption, thereby leading to reduced energy consumption in main memory. Further details regarding bitline energy consumption can be found in “VLSI Memory Chip Design” by K. Itoh, Springer Series in Advanced Microelectronics, 2001, pp. 117–123.